Implantable electrochemical sensors have become an important tool for analyzing and quantifying the chemical composition of a patient""s blood. For example, glucose sensors are generally employed to measure blood glucose levels in patients having diabetes. Such measurements may be used to monitor patient condition, as well as to modify a treatment regimen which typically includes the regular administration of insulin. Thus, blood glucose readings are particularly useful in optimizing therapy.
Electrochemical sensors may be used to obtain periodic readings over an extended period of time. For example, small, flexible subcutaneous sensors are available for chronic implant to perform measurements over time. Such subcutaneous sensors are manufactured using thin film mask techniques. Sensors manufactured according to this process include thin film conductive elements encased between flexible insulative layers of polyimide sheets or similar material. These sensors typically include a plurality of exposed electrodes at one end for subcutaneous placement within a user""s blood. The other end of the sensor generally includes a corresponding exposed plurality of conductive contacts that are adapted to be coupled to a monitoring device. Typical thin film sensors are described in U.S. Pat. Nos. 5,390,671, 5,391,250, 5,482,473, and 5,586,553.
Conventional implantable sensors of the type described above have several disadvantages. Such sensors are generally adapted to be located in contact with subcutaneous tissue for an extended length of time. Extended contact with bodily fluids may cause electrodes provided by the sensors to degrade, resulting in inaccurate sensor readings. Additionally, conventional implantable sensors are generally susceptible to electromagnetic interference, degrading sensor performance. Finally, because of the limited communication capabilities associated with most sensors, direct remote monitoring of sensor signals is not possible, and some intermediate device is necessary to provide the long-range communication capability.
What is needed, therefore, is an improved subcutaneous sensor that addresses the foregoing disadvantages.
The present invention provides an improved implantable sensor system for sensing signals within a living body. The system includes an array of sensors. One or more of the sensors in the array is associated with a protective member that prevents the associated sensor from interacting with the surrounding environment. At a selected time, the protective member may be disabled, thereby allowing the sensor to begin operating to provide sensed signals. In one embodiment, the protective member is formed of a conductive material that can oxidize, is biocompatible, bio-absorbable, and that may be dissolved in solution such as blood upon application of an electric potential. For example, a sensor may be formed within a well of a substrate that is capped by a conductive material such as a biocompatible metal or an electrically-erodible polymer. In another embodiment, the protective member is formed using a material that dissolves over a predetermined period of time. By selecting a variety of materials to form the protective members, various sensors are activated over time to extend the life of the sensor system.
At a given time, one or more activated sensors from the sensor array may be utilized to sense signals that are then processed to provide a more accurate indication of a biological or other condition. For example, signals from multiple activated sensors may be averaged. Alternatively, a voting scheme may be utilized such that one or more signals are discarded prior to obtaining an average signal value. Any other processing scheme may be utilized to obtain a measurement that may then be used to monitor a patient""s condition, or modify therapy delivery.
In one embodiment, the sensor system includes a therapy delivery system for providing therapy based on one or more of the sensed signals. The therapy delivery system may include a drug pump, a circuit to provide electrical stimulation to tissue, or any other type of therapy delivery means known in the art.
According to one aspect of the invention, the disclosed sensor system includes a sensor to sense a biological indicator, and a protective member located adjacent the sensor to shield the sensor from a surrounding environment for a selectable time period. According to another aspect of the invention, a method of sensing signals within a living body is disclosed. The method includes providing a sensor, providing a protective member to prevent the sensor from interacting with the living body, selectively disabling the protective member, and obtaining at least one signal from the sensor. Other aspects of the invention will become apparent from the following description and the attached drawings.